Online type UPSs are widely used on all kinds of power supply occasions. A UPS circuit of the type generally includes three portions.
A first portion is an alternating-direct current conversion circuit, that is, a rectifying circuit, for converting an alternating current into a direct current.
A second portion is an inversion circuit for inverting a direct current to an alternating current.
A third portion is a direct current-direct current circuit for converting a voltage of a battery into a direct current voltage required by the inversion circuit of the second portion.
A UPS charger is a charging apparatus for charging the battery mounted on the UPS of the third portion.
At present, in designs of the UPS charger, generally two manners are adopted.
One is an isolation manner, for example, a conventional flyback isolation circuit, a forward isolation circuit, or another isolation circuit is used as a charging circuit. In this manner, an isolation conversion volume is large and costs are relatively high.
The other is a non-isolation manner, for example, a conventional single BUCK circuit, a dual BUCK circuit, or a BUCK three-level circuit.
The battery mounted on the UPS is closely related to a topology of a main circuit. In order to improve efficiency and lower costs, the mounted battery is integrated with the main circuit. Therefore, the UPS charger usually adopts the non-isolation manner.
The following introduces a UPS charger in the non-isolation manner in the prior art with reference to the accompanying drawings. In FIG. 1, FIG. 2, and FIG. 3, a positive bus BUS+, a negative bus BUS−, and an N wire are output ends of a rectifying circuit.
Referring to FIG. 1, FIG. 1 is a circuit diagram of a UPS charger with a single BUCK topology in the prior art.
As shown in FIG. 1, inputs of the topology are a BUS+ and a BUS−.
A working principle of the topology is: when a switch tube Q1 is turned on, a current flow direction is (BUS+)-Q1-L1-BAT-(BUS−), the BUS+ and the BUS− charge the BAT through the L1, and the L1 stores energy at the same time; when the Q1 is cut off, a current flow direction is L1-BAT-(BUS−)-D1 and the L1 releases the energy to charge the BAT.
Disadvantages of a topology of the type are: the inputs are connected to the BUS+ and the BUS− and input voltages are relatively high, causing relatively high voltage resistance of the device models in the BUCK topology. In this case, costs are relatively high, loss is relatively large, and efficiency is low.
Referring to FIG. 2, FIG. 2 is a circuit diagram of a UPS charger with a dual BUCK topology in the prior art.
The dual BUCK topology refers to two superposed single BUCK topologies. The UPS charger includes two batteries: a BAT1 and a BAT2.
As shown in FIG. 2, inputs of the topology are a BUS+, a BUS−, and an N wire.
Working principles of the topology include the following:
1) In a positive semi-cycle of a power grid voltage, a second switch tube Q2 is turned off and a first switch tube Q1 works.
When the Q1 is turned on, a current flow direction is (BUS+)-Q1-L1-BAT1-N, the BUS+ charges the BAT1 through the L1, and the L1 stores energy at the same time.
When the Q1 is cut off, a current flow direction is L1-BAT1-N-D1 and the L1 releases the energy to charge the BAT1.
2) In a negative semi-cycle of the power grid voltage, the Q1 is turned off and the Q2 works.
When the Q2 is turned on, a current flow direction is N-BAT2-L2-Q2-(BUS+), the BUS− charges the BAT2 through the L2, and the L2 stores energy at the same time.
When the Q2 is cut off, a current flow direction is N-BAT2-L2-D2 and the L2 releases the energy to charge the BAT2.
Compared with the single BUCK, a topology of the type has the following advantages: the inputs are connected to the BUS+, the BUS−, and the N wire and input voltages are low, a device with low voltage resistance may be selected as the device in the BUCK topology. However, disadvantages of the topology of the type are: two sets of BUCK circuits are required, the number of devices is large, and two groups of batteries (the BAT1 and the BAT2) are also required, so the costs are relatively high. In addition, when a voltage of the BUS is relatively low, a requirement for charging the batteries cannot be satisfied. For example, when a voltage of a single side BUS (between the BUS+ and the N wire, or between the BUS− and the N wire) is lower than a voltage of a battery, the battery cannot be charged.
Referring to FIG. 3, FIG. 3 is a circuit diagram of a UPS charger with a BUCK three-level topology in the prior art.
As shown in FIG. 3, inputs of the topology are a BUS+, a BUS−, and an N wire.
Working principles of the topology include the following:
1) In a positive semi-cycle of a power grid voltage, a second switch tube Q2 is turned off and a first switch tube Q1 works.
When the Q1 is turned on, a current flow direction is (BUS+)-Q1-L1-BAT-D2-N, the BUS+ charges the BAT through the L1, and the L1 stores energy at the same time.
When the Q1 is cut off, a current flow direction is L1-BAT-D2-D1 and the L1 releases the energy to charge the BAT.
2) In a negative semi-cycle of the power grid voltage, the Q1 is turned off and the Q2 works.
When the Q2 is turned on, a current flow direction is N-D1-L1-BAT-Q2-(BUS−), the BUS− charges the BAT through the L1, and the L1 stores energy at the same time.
When the Q2 is cut off, a current flow direction is L1-BAT-D2-D1 and the L1 releases the energy to charge the BAT.
Disadvantages of the topology are: a negative end of the BAT is connected to the Q2. In this way, the BAT can be easily interfered by a high-frequency switch wave of the Q2. The N wire is also interfered by the high-frequency switch wave. In this case, battery performance and electromagnetic compatibility of a whole circuit may be affected.